The present invention relates to the storage of hydrogen and, more particularly, to novel alloys capable of reversible sorption of hydrogen.
Hydrogenn gas has been considered as an alternate fuel for various types of power sources, such as internal combustion engines, gas turbines, fuel cells, and the like. Its attractiveness as a fuel stems from the fact that it can be produced using various essentially inexhaustible energy sources, i.e., solar, nuclear, and geothermal; and that it is essentially nonpolluting. One of the primary problems relating to the use of hydrogen as a fuel is in regard to its storage over extended periods of time. Conventional storage methods, such as compression and liquefaction in pressure vessels, are not satisfactory due to the danger of fire and explosion.
A promising approach to the problem of hydrogen storage lies in the use of metal alloys which are capable of reversible sorption of hydrogen. A number of metal alloys have previously been proposed for the solid state storage of hydrogen in the form of metal hydrides. Among such metal alloys disclosed in the prior art are iron-titanium alloys (Wiswall, Jr., et al., U.S. Pat. Nos. 3,508,414 and 3,516,263), and modifications thereof with manganese (Reilly, et al., U.S. Pat. No. 3,922,872) and/or vanadium (Liu, U.S. Pat. No. 4,111,689). The modification with manganese is taught by the Reilly, et al. patent to increase the hydrogen storage capacity of the alloy and to reduce the dissociation pressure of the metal hydride. The vanadium-containing alloys disclosed in the Liu patent have a vanadium content ranging from about 5 to 33 percent by weight, and are taught to eliminate the necessity for elevated temperatures during the hydrogen sorption operation.
One of the problems associated with all of the above-described prior art iron-titanium-based alloys is the inability of their hydrides to release substantially all of the desorbable hydrogen at a substantially constant pressure at a given temperature. This hydrogen storage characteristic of the metal alloy may be readily determined by examining the desorption isotherm of the metal hydride, which is obtained by plotting the dissociation pressure of the hydride at a constant temperature against its H/M ratio, which is defined as the ratio of total hydrogen atoms to total metal atoms in the hydride. For practical use as a hydrogen fuel source, the metal hydride should ideally exhibit a room temperature desorption isotherm having a long, flat plateau somewhere between 1 to 10 atmospheres and extending over substantially the entire range of H/M ratios. The desorption isotherms of the metal hydrides of all of the above-described prior art iron-titanium-based alloys, at best, exhibit two distinct plateaus, one considerably higher than the other, indicating a substantial variation in the hydrogen release pressure at a given temperature as the hydrogen content of the metal hydride becomes diminished.